l 6 - geographic data bases

L 6. Geographic Databases 1

Introduction to Geoinformatics

L-6. Creating and Maintaining Geographic Databases

Dr. Gyrgy SZAB associate professor

Budapest University of Technology and EconomyDepartment of Photogrammetry and Geoinformatics

[email protected]

ContentsOVERVIEW

After people, the database is arguably the most important part of a GIS because ofthe costs of collection and maintenance, and because the database forms the basis of all queries, analysis, and decision making.

LEARNING OBJECTIVES Understand the role of database management systems in GIS; Recognize structured query language (SQL) statements; Understand the key geographic database data types and functions; Be familiar with the stages of geographic database design; Understand the key techniques for structuring geographic information, specifically

creating topology and indexing; Understand the issues associated with multi-user editing and versioning.

Longley, Goodchild, Maguire, Rhind (2011): Geographical Information Systems and ScienceCH 10. pp. 251-274.

The six component parts of a GIS

Data

Software

Procedure

Data Base Management Systems Limitation of the analog libraries: storage place, limited

access, problematic retrieving Limitation of the traditional data repositories: structural

and storage are dissimilar, verification, consistency weak, slow retrieval, limited user access, restricted application of data

Database Management Systems: Standardized, structured digital storage, verified, controlled access, fast retrieval, Wide range access and application

Physical/Logical/Structural independency, Security management, authorization

Web & Application Services

Data Management Services

USER level

WEB services

Integrated Data Base Management

Typical GIS ArchitectureDBMS Data Models

History: File storage: physical storage: records, fields, keys Hierarchical model: logical hierarchy explicitly stored by

pointers Network model: cross connections between hierarchical

elementsPresent: Relational model (RDBMS): 2D tables, fields, keys, foreign

keys, relations, functions, normalisation Object-oriented model(ODBMS): near to real world model

encapsulation, objects sets, inheritance, polymorphisms, methods

Object-Relational (ORDBMS): hybrid solution to extent the RDBMS engine with ODBMS object management


Files

Phisycal storage: Developement dependency Weak consistency: insert, delete, modify Fix, variable record size

Hierarchical Model Explicit

Connections -Pointers

Logical hierarcy

Redundancy Sensitivity

Network Model

Explicit Connections -Pointers

Cross connection No redundancy Sensitivity

Relational Database Management System - RDBMS

Standardised storage: 2D Tables, Field, Entities, Keys Components: Relational functions, Tables, Integrity

constrains Consistency, Security, Authorisation SQL language

Object Oriented Model Near to Real

World Model Ecapsulation Objects sets Inheritance Polymorphism Methods High

Consistency

The roles of GIS and DBMS


Storing Data in DBMS Tables The lowest level of user interaction with a geographic database is usually the object

class (also called a layer or feature class), which is an organized collection of data on a particular theme

Object classes are stored in a standard database table, a two-dimensional array of rows and columns.

Rows contain objects (instances of object classes) Columns contain object properties or attributes The data stored at individual row, column intersections are usually referred to as values. Geographic database tables are distinguished from non-geographic tables by the

presence of a geometry column. Tables are joined together using common row/column values or keys. Following joins, all tables can be treated as a single table Lists Codds five principles for the efficient and effective design of tables and

introduces the concept of normal forms Normal forms improve the simplicity and stability of a database and reduce redundancy

of tables by splitting them into sub-tables that are re-joined at query time

Parts of GIS database tables for U.S states (A) STATES table; (B) POPULATION table

Parts of GIS database tables for U.S states(C) joined tableCOMBINED STATES and POPULATION

(B) cleaned data in a GIS DBMS

Tax assessment database

(A) raw data

Tax assessment database

(D) joined table

(C) data partially normalized into three subtables

SQL QuerySQL Simple /Standard Query Language ISO 9075 There are three key types of SQL statements:

DDL (data definition language) used to create, alter and delet relational databasestructures

DML (data manipulation language) used to retrieve and manipulate data DCL (data control language) handle authorization and access

Simple Queries in Geomedia: ANALYSIS->ATTRIBUTE QUERY based on the selected feature class attributes creation a general SQL QUERY in the FILTER field:

The general sintax:SELECT FROM [WHERE ][][];


Find Parcels where Value is greater than 300,000 $ and

the zoning type is Residental

SELECT Tab10_3a.ParcelNumb, Tabl0_3c.Address,Tabl0_3a.AssessedValue FROM (Tabl0_3b INNER JOIN Tabl0_3a ON Tabl0_3b.ZoningCode =Tabl0_3a.ZoningCode) INNER JOIN Tabl0_3c ON Tabl0_3a.OwnersName = TablO_3c.OwnerName WHERE (((Tabl0_3a.AssessedValue) >300000) AND ((Tabl0_3b.ZoningType) ="Residential"));

Results of a SQL query against the tables in Figure 10.3C

Geographic Database Types and Functions

The geometry class hierarchy Testing spatial relationships between these geometric objects (there are

nine methods) Each takes as input two geometries and evaluates whether the

relationship is true or not. The full set of Boolean operators to test the spatial relationships

between geometries is: Equals, Disjoint, Intersects, Touches, Crosses, Within, Contains, Overlaps, Relate

Methods support spatial analysis on these geometries: Distance, Buffer, ConvexHull, Intersection, Union, Difference, SymDifference

Geometry class hierarchy(Source: after OGC 1999, reproduced by permission of Open Geospatial Consortium, Inc.)

Examples of possible relations for two geographic database operators

(Source: after Zeiler 1999)


Examples of spatial analysis methods on geometries


The Database Design ProcessConceptual model Model the users view Define objects and their relationships Select geographic representationLogical model Match to geographic database types Organize geographic database structurePhysical model Define database schema

Stages in database design


Four levels of data model available for use in GIS projects in Users view

Object hierarchy Object Super Class Object Sub Class-1

Object Sub Class-n

Object Set

6000 7000 8000 9000

7200

7240

Boundary Trafic Vegetation Hidrology

VaterTerestrialAerial

7210 7220 7230

Highway Mani road Unpaved road

Secondary r.

7221 7222 7223

Gov. Municipal Private

Object propertiesObj.

Geometry Attributes

vector raster

Metr. Top. Doc. Fact

Object Catalog TableObject Name -Feature Class

ObjectHierarchy

Geometry Legend Attributes Req. Geom.accuracy

Main_line W_net L ID, material, diameter, pressure, build_date, soil,

Sec_line W_net L ID, material, diameter, pressure, user_name

Stopcock W_net P ID, diamater1, diameter2, pressure

Parcel User A ID, parc_id, owner, adress, consumption

Block User A ID, Block_name, unit_price

Public_area Municipal A ID, Street_name

Error Event P ID, Name, Err_type, date, Damage_cost


Structuring geographic information Topology creation

Normalized Model focuses on the storage of an arc-node data structure (ArcGIS): Normalized because each object is decomposed into individual topological primitives

for storage in a database and then subsequent reassembly when a query is posed. Normalized approach advantages are: similarities to the familiar arc-node concept,

geometry is only stored once, access can be via an SQL API Normalized approach disadvantages are: query performance suffers, standard

referential integrity rules in DBMS have no provision for the complex topological relationships, updates are problematic due to cascading effects

Physical Model topological primitives are not stored in the database and the entiregeometry is stored together for each object (Geomedia):

Only other things required to be stored are the specific set of topology rules Topological relationships are then computed on-the-fly whenever they are required by

client applications. Requires an external client or middle-tier application for validating topological

integrity

Normalized database topology model

Physical database topology model

Indexing Geographic databases tend to be very large and geographic queries

computationally expensive Indexes speed up searching by allowing random instead of sequential

access.

A database index is, conceptually speaking, an ordered list derived from the data in a table.

DBMS one-dimensional B-tree (Balanced Tree) index that is found in most major commercial DBMS.

Since these 1D indexes are very poor at indexing geographic objects, several geographic indexing techniques have been developed(Quadtree, R-Tree)

An example of a B-tree index A multilevel grid geographic database index


The point quadtree geographic database index

(Source: after van Oosterom 2005. Reproduced by permission of John Wiley & Sons, Inc.)

The region quadtree geographic database index

(Source: www.cs.umd.edu/~brabec/quadtree. Reproduced by permission of Hanan Smaet and Frantisek Brabec)

Linear quadtree search orderThe R-tree geographic database index

(Source: After van Oosterom 2005. Reproduced by permission of John Wiley, Inc.)

An MBR can be used to determine objects definitely in the study area (green) because of no overlap, definitely out (yellow), or possibly in (blue). Objects possibly in can then be analyzed further using their exact geometries. Note the red object that is actually completely outside, although the MBR suggests it may be partially within the study area

Area in area test using MBREditing and Maintenance

Editing is the process of making changes to a geographic database by adding new objects or changing existing objects as part of data load or database update andmaintenance operations.

A database update is any change to the geometry and/or attributes of one or more objects or any change to the database schema.

Contemporary GIS come equipped with an extensive array of tools for creating and editing geographic object geometries and attributes.


Multi-user editing of continous databases

Transactions A group of edits to a database is referred to as a

transaction. Many geographic transactions extend to hours, weeks, and

months, and are called long transactionsVersioning Identifies two kinds of versioning Pessimistic locking locks out all but one user during an

update operation Optimistic versioning allows multiple users to update at

the same time

Database transactions

(A)linear short transactions

(B) branching version tree

Version reconciliation

For Version 5 the user chooses via the GUI the geometry edit made in Version 3 instead of 1 or 4.

Thank You

MerciGrazie

Gracias

Obrigado Danke

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l 6 - geographic data bases

Documents

geographic information

relational model rdbms

keys hierarchical model

geographic databasesdr

security management

pointers network model

storing data

file storage